Research objectives: We will record from single neurons of limbic system in unrestrained rats. 1. Behavioral correlates of neuronal firing and firing repertoires of neurons in dorsal hippocampal formation will be determined in a semi naturalistic colony of rats. 2. Behavioral correlates of neuronal firing and firing repertoires will be determined in non-naturalistic conditions in ventral hippocampal formation, entorhinal cortex, and cingulate gyrus. 3. The relation of neuronal firing to slow wave Theta rhythm will be determined in dorsal hippocampal formation. 4. We will electrically stimulate perforant path, fornix-fimbria, and homotopic contralateral dorsal hippocampus and record from single neurons in dorsal CA1, CA3, and fascia dentata, all in the same lamella. We will determine the electrophysiology of neurons of known behavioral type, and how these change in different behaviors, in hippocampal seizures, and with systemic administration of drugs. The overall objective is to determine the mechanisms of the processing of information in hippocampal formation.